Retaining walls are subject to various forces that may cause them to fail. Pressure at the toe of the footing is generally larger than pressure at the heel of the footing so retaining walls have an inherent tendency to tilt forward away from an embankment. Occasionally, the base soil is of a poor quality and when sufficient backfill is placed between the backface of the retaining wall and an embankment, for example, the approach fill at a bridge abutment, the backfill pressure produces a settlement with lateral effect into the zone beneath the heel so that the retaining wall may tilt back into the backfill and the embankment. Lateral forces generated by earth and water pressure may cause the base of the retaining wall to slide outward and fail. Retaining walls are generally designed to resist these lateral forces by creating friction between the bottom surface of the footing and the soil. Some soil types are more prone to shifting or erosion and may decrease the friction between the footing and soil. Different soil types exert different amounts of pressure on the retaining wall. Local soil conditions may require an increase in the width of the footing to achieve the required friction between the bottom surface of the retaining wall and the soil to counteract the lateral forces on the retaining wall. However, making the footing wider increases the amount of materials used, increases transportation costs, and requires increased excavation of soil to form a wider subgrade which increases cost and time required for site preparation and installation. In some cases, it may not be possible to increase the footing width based on site requirements. The depth of the footing cover can also be increased in some situations to provide additional resistance to lateral forces; however, this also increases the cost of site preparation because excavation must be deeper, and additional concrete is required which increases costs as well.
Concrete retaining walls that are cast-in-place at the job site are known to have a higher coefficient of friction between the footing and the soil compared to precast concrete retaining walls that are manufactured at a precast plant, transported to the job site, and placed on the soil. However, there are several shortcomings in the use of cast-in-place retaining walls compared to the use of precast concrete retaining walls. Creating forms for a retaining wall at a job site is time consuming and may require the presence of many employees at a remote location. The job site may not be as safe for employees as a precast plant due to open excavations, the presence of heavy equipment, and the natural environment. The forms may have to be custom made, increasing labor and material costs and making re-use of the forms unlikely. Placing and aligning reinforcing steel precisely at a job site may be more difficult than at a precast plant, potentially weakening the retaining wall. The concrete for the retaining walls may have to be transported long distances to the job site in individual truckloads increasing transportation and labor costs. Finally, the concrete is exposed to the environment while it is curing which can increase the curing time or adversely affect the strength characteristics of the retaining wall. Construction of the project may be delayed while waiting for the concrete to cure.
Due to the numerous limitations associated with cast-in-place retaining walls, there is an unmet need for a precast concrete retaining wall which has a coefficient of friction equivalent to a cast-in-place retaining wall of similar size.